The increasingly strict legal provisions relating to permitted pollutant emissions from vehicles containing internal combustion engines mean that it is necessary to minimize pollutant emissions as far as possible when the internal combustion engine is operating. This can be achieved on the one hand by reducing the pollutant emissions resulting during combustion of the air/fuel mixture in the respective cylinder in the internal combustion engine. On the other hand exhaust gas treatment systems are used in internal combustion engines to convert the pollutant emissions produced during the combustion process of the air/fuel mixture in the respective cylinders to harmless substances. Catalytic converters, which convert carbon monoxide, hydrocarbons and nitrogen oxide to harmless substances, are used for this purpose. A very precisely adjusted air/fuel ratio in the respective cylinder is required both to influence the production of pollutant emissions during combustion in a specific fashion and for the exhaust gas catalytic converter to convert the pollutant components with a high level of efficiency.
DE 199 03 721 C 1 discloses a method for a multicylinder internal combustion engine for regulating an air/fuel mixture to be burned in a cylinder-selective fashion, in which the lambda values for different cylinders or cylinder groups are detected
and regulated separately. An individual regulator is assigned to every cylinder. This regulator is configured as a PI or PID regulator, its controlled variable is a cylinder-specific lambda value and its reference variable is a cylinder-specific target lambda value. The manipulated variable of the respective regulator then influences fuel injection in the respectively assigned cylinder.
EP 0 802 316 B 1 also discloses a method for controlling an internal combustion engine, with a regulator configured as a PID regulator, the controlled variable of which is an estimated value for a cylinder-specific air/fuel ratio determined by an observer and the reference variable of which is a correspondingly converted mean lambda control factor, evaluated with a target air/fuel ratio. The mean lambda control factor is determined by taking the mean of all the cylinder-specific lambda control factors. Each cylinder-specific lambda control factor is the manipulated variable of the respective PID regulator assigned to the cylinder. A corrected injection time is determined by multiplying an injection period predefined for all the cylinders in the internal combustion engine by the respective cylinder-specific lambda control factor.